Continuum Approach Toward Modeling the Mechanics of Solid Lubricating Films

摘要

Analyses are developed to predict the tractive forces that will occur in arolling-sliding contact between one body of a single material and a second body containing a thin coating of solid lubricant. Isotropic materials and conditions of plane strain are assumed. The loaded coating thickness is taken to be large compared with asperity heights but small compared with contact dimensions. Contact pressures are assumed to be high compared with the shear yield stress of the coating which in turn is taken to be small compared with those of the substrates. An initial analysis is presented for approximating tractions under conditions of low slide to roll ratios which includes elastic, plastic, creep and thermal interactions. This analysis implements an approach developed for elastohydrodynamic lubrication at pressures and shear rates where the lubricant exhibits solid-like behavior but is oriented toward solid lubrication and includes a more extensive thermal analysis. Solutions are presented which show the influence of elastic modulus, rheological model, yield stress and pressure and temperature dependence of mechanical properties on predicted traction and shear stress behavior. An analysis is presented which reduces the Levy-Von Mises equations for a plastic-rigid system so as to approximate thin film behavior under conditions of high slip rate. This analysis shows the expected development of a nearly hydrostatic state of stress for the coating in the contact zone but also shows that the film cannot support a pressure gradient when yielding occurs inside the coating.